1. Field of the Invention
This invention relates to an angular position sensing and control apparatus and method and more particularly to such a position sensing and control system which is free of spurious signals contained in the outputs of the sensors in the system due to accelerations which are nondeterminative of angular position.
2. Description of the Prior Art
Difficulty has been experienced in the past in monitoring the angular orientation of a structural body with reference to earth's coordinates and in controlling a platform or other moveable part mounted within the body to maintain a predetermined orientation referenced to earth coordinates while the structural body experiences three dimensional angular and translational motion. The usual approach for monitoring orientation or stabilizing a platform involves the use of a vertical gyro with its attendant disadvantages stemming from its relatively short operating life and deteriorating accuracy as the spinning rotor and gimbal bearings deteriorate with extended use. The wear out life time of the vertical gyro represents a serious and significant problem of periodic replacement as well as a danger or loss of date or erroneous platform position control due to untimely and enexpected gyro failure modes.
Attempts have heretofore been made to control the attitude of one part of a machine with respect to some reference. For example, attempts have been made to control the attitude of the one part by utilizing electrolytic potentiometers or linear accelerometers to provide a gravity-referenced local horizontal. This serves to sense linear acceleration only, and has been found to have numerous disadvantages due to error injection as accelerations other than acceleration of gravity are sensed. Angular acceleration sensors with double integrated output produce an angle indication, but errors due to linear acceleration. sensitivity of the angular accelerations sensor are produced.
There is a need for an angular position sensing and control system which is not subject to the stringent structural replacements placed on component parts associated with the high angular velocity spinning rotor of a gyro, and which is free of the errors associated with spurious acceleration sensitivity associated with tilt sensors and angular accelerometers.